GitLab commit comments fail with "old" line_type

The GitLab Documentation [1] states that "In order to post a comment in a particular line of a particular file, you must specify the full commit SHA, the path, the line and line_type should be new. "

Below that the line_type element is stated as accepting "new" and "old" values for line_type. I am trying to comment on old line 461 of e55845be in MR prarit/Test-Lab!2

I can comment in the webUI,

prarit/Test-Lab!2 (e55845be)

but am unable to do so via the API. [Note: https://gitlab.com/prarit/Test-Lab should be publicly visible.]

For example,

curl --request POST --header "PRIVATE-TOKEN: <my_secret_token>" --form "note=Hello old line" --form "file=Makefile" --form "line=461" --form "line_type=old" https://gitlab.com/api/v4/projects/21681515/repository/commits/e55845bedfe55a439cea4eab508998f85bef7b5d/comments

fails to apply the comment to old line 461 of the Makefile, and instead applies the comment to the entire commit. This implies an error, however, I am unable to see one as the information contained within the values appears to be correct.